1. Field of the Invention
The present invention relates to light-emitting diodes (LEDs) structures, and more particularly, to an LED structure containing a p-type quantum-spot epitaxial layer grown on a p-type GaN layer. The present invention also relates to a manufacture method for the LED.
2. The Prior Art
Because the refractive index (n) of gallium nitride (GaN) semiconductor as an LED material is 2.3 approximately, far different from that of air (n=1), a small critical angle of total reflection about 25° exists to block almost all the incident rays emitted from a light-emitting layer of LED.
For improvement, a known method according to IEEE Transactions on Electron Devices, 47(7), 1492, 2000 was presented to coarsen a semiconductor surface, particularly an epitaxy surface to raise the scattering and refracting probability of incident light usually by way of etching. U.S. Pat. No. 5,040,044 discloses a chemical etching process for coarsening a light-emitting clement to improve tight emitting efficiency. Besides, there are other similitudes, such as U.S. Pat. Nos. 5,429,954 and 5,898,192. However, the mentioned processing method is applicable only to the red-light LED, not to GaN-based materials which are especially weak in resistance against acids/alkalis, and it is relatively difficult to control a wet etching process while a dry etching process is liable to spoil the epitaxial layer and cause an increment of impedance, particularly in the case of a P-type GaN layer, to thereby affect the current distribution and degrade the light-emitting efficiency. In addition, because the deposited p-type GaN layer is extremely thin (only 0.1–0.3 μm), the light-emitting layer could be impaired occasionally by a direct coarsening to result in a smaller light-emitting area. For promoting permeability, the transparent electrode on a GaN LED should be made as thinner as possible (about 10 nm) so that a direct coarsening job might destroy the transparent thin electrode or make it discrete to badly affect the current distribution and light-emitting efficiency. On the other hand, though the dry etching process is applicable to a p-type GaN layer having a sufficient thickness, the current distribution and light-emitting efficiency is nevertheless deteriorated to hence set the coarsening process in a dilemma.